This invention relates to rotating machines, e.g. rotary compressors, and is more especially directed to scroll compressors for refrigeration and air conditioning systems, and in which an electric motor is formed of a rotor and a stator in a tubular shell, with the rotor being arranged to drive a scroll compression mechanism. The invention is also directed to the construction of a compressor of this type which facilitates precise alignment of the bearings and stator, so that the rotor assembly can be easily installed in precise alignment with respect to the stator and with respect to upper and lower bearings in which the crankshaft is journalled.
Scroll type rotary machines are used to compress or to pump a gas, and these devices typically have two scroll members each formed of a generally circular end plate and a spiral or involute wrap. The scroll members maintain a fixed azimuth relative to one another but are radially offset so that one orbits about the other. Both wraps interfit to maintain contact at surfaces of the other element, such as to define crescent shaped volumes that move towards the center of the pair of scrolls and become smaller as one scroll member orbits the other.
Relative orbital motion is typically obtained by holding one scroll member fixed in the shell, and orbiting the other by rotating an eccentric crankshaft and holding the orbiting scroll member with an anti-rotation device, e.g., an Oldham ring.
The driven orbiting scroll member, being offset from the axis of the crankshaft, represents an unbalanced torsional load. Even though this is compensated by an eccentric counterweight, there are couple forces acting on the crankshaft when the compressor is at operating speeds.
The drive motor for the compressor has an annular stator armature that is positioned in the compressor's tubular shell, and a generally cylindrical rotor that fits into a cylindrical passage in the stator. To obtain top operating efficiency, the air gap between the rotor and the wall of the passage in the stator should be assymmetrical as possible. The rotor must be held strictly in alignment with the stator for this air gap to be adequately aligned. Also, the crankshaft must be rather precisely supported by the bearing system so that the crankshaft and its associated eccentric drive move the orbiting scroll member in a precise orbiting motion relative to the fixed scroll member. Additionally, to reduce couple forces on the crankshaft, the bearing that supports the upper end of the crankshaft should not extend to far down the crankshaft, so that the rotor counterweight can be positioned as high on the crankshaft as possible.
However, supporting both the upper and lower ends of the crankshaft in bearings means that one of these bearings cannot be installed in the shell until after the rotor assembly is installed. Consequently, this means that it is difficult or impossible to obtain precise alignment of the rotor assembly relative to the stator and upper bearing, because it is difficult or impossible to align the lower bearing precisely with respect to the stator and the upper bearing.